This invention relates to novel copoly(arylene ether ketone) having a biphenylene-4,4'-dicarbonyl group in their backbone and to methods for their preparation.
Poly(arylene ether ketones) possess many desirable properties, for example, high temperature stability, mechanical strength, and resistance towards common solvents. They are thermoplastics, facilitating their melt fabrication into articles of diverse sizes and shapes. Many are crystalline and retain substantial mechanical properties up to or about their melting temperatures (Tm), which typically are above 300.degree. C.
While a high Tm is desirable for this reason, too high a Tm is undesirable, because a crystalline poly(arylene ether ketone) must be melt processed at a temperature substantially above its melting point--commonly at least 30.degree. C. above. However, poly(arylene ether ketones) begin decomposing more or less rapidly at about or above 400.degree. C., so that a poly(arylene ether ketone) having a Tm in the near 400.degree. C. would be difficult to melt process without decomposition. For instance, Berr, in U.S. Pat. No. 3,516,966, reports that the polymer from diphenyl ether and terephthaloyl chloride (Tm 385.degree. C.) cannot be practicably melt-processed because it requires an extrusion temperature of 420.degree. C. or higher, but decomposes at temperatures in excess of 400.degree. C. Further, conventional melt processing equipment is frequently not designed for operation at temperatures above 400.degree. C., making specially designed equipment necessary. In view of these considerations, it is desirable for a poly(arylene ether ketone) to have a Tm below about 370.degree. C.
The high-temperature mechanical properties of a poly(arylene ether ketone) are also influenced by its glass transition temperature, or Tg, There is a significant loss in mechanical properties at about or above the Tg, even though for crystalline poly(arylene ether ketones) substantial mechanical properties may still be retained up to the Tm. For a many applications, substantial retention of room temperature properties at 150.degree. C. or above is a requirement. Because of the phenonmenon known as densification embrittlement, in which a polymer densifies and embrittles at about its Tg, merely having a Tg at or about 150.degree. C. is insufficient. To avoid densification embrittlement, the Tg should be be significantly above 150.degree. C., preferably about 165.degree. C. or above. Combining the above factors, a poly(arylene ether ketone) having a Tg about or above 165.degree. C. and a Tm about or below 370.degree. C. is highly desirable.
The characteristics of a poly(arylene ether ketone)--Tg, crystallinity, Tm, chemical resistance, etc.--depend on a number of parameters: the ether-to-ketone ratio, the sequencing of subunits, linearity, the presence of meta-substituted and/or non-phenylene arylene groups, and the like. Poly(arylene ether ketones) representing various combinations of these parameters are known. See, for example, Marks, in U.S. Pat. No. 3,441,538; Rose et al., in U.S. Pat. No. 4,320,224; Dahl, in U.S. Pat. Nos. 3,953,400 and 4,111,908; and Dahl et al., in U.S. Pat. No. 3,956,240. This is a continuing search for new polymers of this class having particularly advantageous properties for a desired end use.
Berr, cited supra, illustrates prior art attempts to tailor the Tm of a poly(arylene ether ketone) by altering its molecular composition and the fact that often such manipulations represent trade-offs in which a gain in one property is at the expense of a loss in another property. Noting that the poly(arylene ether ketone) ##STR4## was not melt-processable because of its high Tm, he partially replaced one monomer (terephthaloyl chloride) with another (isophthaloyl chloride). He was able to obtain a melt-processable copoly(arylene ether ketone) having the repeat units ##STR5## But the meta-phenylene group reduced the crystallinity of the copolymer, so that copolymers having more than 30 mole % isophthaloyl chloride-derived repeat units crystallized only with difficulty. These results illustrate the negative effects of disruptions in the regularity of the polymer backbone. Also, the meta-phenylene group is generally not as thermally and/or chemically stable as para-phenylene, so that mixed para-/meta-copolymers are less stable than their all-para counterparts.
Staniland, in published European application EP No. 184,458,A2, illustrates another attempt to modify the Tm and/or the Tg of a poly(arylene ether ketone) by copolymerization. He noted that while the poly(arylene ether ketone) ##STR6## has a Tg of 143.degree. C. and a Tm of 334.degree. C., he was able to lower its Tm by preparing a copolymer in which the second repeat unit ##STR7## was introduced. For example, the copolymer combining these two repeat units exhibits a minimum in the Tm at about 20 mole % of the second repeat unit (309.degree. C.). Thus, the second repeat unit (whose homopolymer has a Tg of 167.degree. C. and a Tm of 416.degree. C.) has the effect of lowering the Tm. However, the Tg of Staniland's copolymers remains below or about 150.degree. C. and does not rise significantly above this value until the mole % of the second repeat unit is very high, by which time the Tm has also risen to an undesirably high value.
Staniland's copolymer has an ether-to-ketone ratio of 2:1. It has generally been observed that poly(arylene ether ketones) having lower either to ketone ratios, e.g. 1.5:1 or lower, have higher Tg's and are more chemically resistant. Since Staniland's Tm lowering repeat unit has an ether-to-ketone ratio of 2:1, insertion of such a repeat unit into a poly(arylene ether ketone) having an ether-to-ketone ratio of 1.5:1 or lower, would undesirably raise the ether-to-ketone ratio and lower its Tg.
Further, it is known that in poly(arylene ether ketones) a phenylene group flankes by two ether groups is chemically reactive under certain conditions, for example being readily sulfonated, because the electron denoating (activating) effect of the two ether groups is not counteracted by an electron withdrawing groups. Since in a biphenylene group flanked by two ether oxygens the same considerations apply, it is unattractive for incorporation into copoly(arylene ether ketones) for applications requiring superior chemical resistance.
This invention provides copoly(arylene ether ketones) having an ether-to-ketone rato of about 1.5:1 or below and Tg's significantly above 150.degree. C.